低温冲击对干热岩裂缝导流能力的影响

Influence of Thermal Shocking on Crack Conductivity in Hot Dry Rock

为了研究干热岩采热过程中低温冲击作用对裂缝导流能力的影响,利用FCS-842导流仪对预热处理后的花岗岩岩板进行导流能力测试,分析了不同低温冲击强度、支撑剂类型、支撑剂粒径和铺砂浓度条件下的裂缝导流能力和支撑剂破碎率变化规律。结果表明:低温冲击造成的裂缝面“软化”对导流能力具有十分重要的影响。一方面,裂缝面经历的低温冲击作用越强(即预热处理温度越高),相同闭合应力下的裂缝导流能力越低。当预热处理温度超过300℃时,导流能力在低闭合应力下发生明显降低;另一方面,裂缝面的软化导致支撑剂嵌入加剧,从而使支撑剂破碎率降低。采用大粒径、高强度支撑剂和提高铺砂浓度,有利于维持干热岩储层压裂裂缝的高导流能力。

In order to study the influence of thermal shocking on fracture conductivity in the process of water circulation heat extraction of dry hot rock,the fracture conductivity of pre-heated granite slabs was tested using FCS-842 fracture conductivity testing system.The influences of preheating temperature,proppant type,proppant particle size and proppant laying density on fracture conductivity and proppant crushing rate are analyzed.Experimental results show that the"softening"of fracture surface caused by thermal shocking has a very important influence on the fracture conductivity.On the one hand,the stronger the thermal shocking effect(i.e.,the higher the preheatingtreatment temperature),the less the fracture conductivity under the same closure stress.When the preheating treatment temperature exceeds 300℃,the fracture conductivity decreases obviously under low closing stress.On the other hand,the"softening"of fracture surface leads to the intensification of proppant embedding,which reduces the proppant crushing rate.Using the proppant with large particle size and high-strength and increasing proppant laying density are conducive to maintaining high conductivity of fracturing fractures in dry hot rock reservoirs.